A plating material provided with a plating layer of tin (Sn), a tin alloy and others on a conductive base such as copper (Cu) and a copper alloy (referred to as a base hereinafter) is known to be a high-performance conductor having excellent conductivity and strength of the base and excellent electrical connectivity, corrosion resistance and soldering quality of the plating layer. The plating material is widely used for various terminals and connectors used in electric/electronic devices. The plating material is normally undercoated with nickel (Ni), cobalt (Co), iron (Fe) and others having a barrier function on the base to prevent an alloy component (referred to as a base component hereinafter) such as zinc (Zn) from diffusing in the plating layer.
When the plating material is used as a terminal in a high-temperature environment such as an inside of an engine room of a vehicle, for example, although an oxide coating film is formed on a surface of the Sn plating layer because the Sn plating layer on a surface of the terminal is oxidizable, the oxide coating film is brittle and breaks down when the terminal is connected and a non-oxidized Sn plating layer is exposed, thereby obtaining favorable electrical connectivity.
Because a fitting-type connector is multipolarized lately with advancement of electronic control, a considerable force is necessary for plugging a male terminal group into/out of a female terminal group. In particular, plugging such a connector is difficult in a narrow space such as the engine room of the vehicle, and it has been strongly demanded to be able to reduce the force for plugging in/out such a connector. Still more, as workability in connecting the connector is improved by reducing the force for plugging in/out the connector, it has been demanded to reduce the force for plugging in/out the connector also from this point of view.
In order to reduce the plugging-in/out force, the Sn plating layer on the surface of the connector terminal may be thinned to weaken contact pressure between the terminals. However, because the Sn plating layer is soft, a fretting phenomenon may occur between contact faces of the terminals, thereby causing inferior conduction between the terminals.
In the fretting phenomenon, the soft Sn plating layer on the surface of the terminal wears and is oxidized, becoming abrasion powder having large specific resistance, due to fine vibration between the contact faces of the terminals caused by vibration and changes in temperature. The lower the contact pressure between the terminals, the more the fretting phenomenon is prone to occur.
In order to assure a low plugging force, Japanese Patent Application Laid-Open No. 2000-226645 Gazette, for example, has proposed a method of forming a hard Cu—Sn intermetallic compound layer that hardly causes the fretting phenomenon on the outermost surface by plating Sn on Cu or a Cu alloy, implementing a reflow process and then treating by heat in an atmosphere at an oxygen concentration of 5% or less. However, the method has had a problem that workability of the plating process is inferior. Japanese Patent Application Laid-Open No. 2000-226645 Gazette has no description about a concentration of Cu—Sn in the Cu—Sn intermetallic compound layer and has had a problem that it is difficult to perform the reflow heat-process in producing in line to adequately form an oxide coating layer with a controlled thickness on the surface of the Cu—Sn intermetallic compound layer.
Further, in order to assure the low plugging force and others, Japanese Patent Application Laid-Open No. 2004-68026 Gazette describes a conductive material for a connecting component that hardly causes the fretting phenomenon, in which a surface plating layer composed of a Ni layer and a Cu—Sn alloy layer is formed on a surface of a base composed of Cu or a Cu alloy in this order. However, the material is also inferior in terms of workability of plating process. Still more, it is difficult to perform the reflow heat-process in producing in line because of the Cu—Sn alloy layer controlled by an average value of the concentration of Cu—Sn.
Japanese Patent Application Laid-Open No. 2004-339555 Gazette describes forming a metal plate layer by plating metal on a surface of a metallic base and forming a plated material mixed with soft regions spreading like a net and a hard region surround by the net of the soft region by a reflow process. However, the plated material has a problem that the Cu component in the base diffuses to the plate uppermost surface and is oxidized, further increasing a contact resistance value.
Japanese Patent Application Laid-Open No. 2006-77307 Gazette describes a conductive material for a connecting component in which a Cu—Sn alloy coating layer composed of particles of several μm in diameter is formed along irregularities of a surface of a base. Further, a Sn coating layer is melt and smoothed, and a part of the Cu—Sn alloy coating layer is exposed on the surface of the material.
When there is no Cu layer in a substrate and a Ni substrate exists, there would be no problem. However, when the Cu layer exists or no Ni substrate exists, even if there would be no problem in an initial state, under an environment in which a connecting component is mounted in an actual car and sliding and thermal loads are applied at the same time, the pure Sn portion is scraped due to sliding and Cu diffuses up to a surface and oxidized, thereby increasing resistance.